Surplus electrical power originating, for example, from renewable energy sources can be stored in the power grid only to a limited degree. This also applies to surplus power which is obtained in fossil power plants when they are running within the optimal economic load range but the power is not being demanded by the consumer from the grid. There are various large-scale storage devices for intermediate storage of this surplus power in relatively large amounts. One of these is, for example, a pumped storage power plant. In the battery sector, one approach for electrical energy storage means is to use rechargeable oxide batteries (ROB), i.e. high-temperature metal/air batteries. In these batteries, a metal-based storage medium is reduced or oxidized according to the state of the battery (charging or discharging). In the course of a multitude of these cyclical charging and discharging operations, i.e. oxidation and reduction operations, of the storage medium, there is a tendency in this medium, at the comparatively high operating temperatures to which such a battery is subjected, which are typically between 600° C. and 900° C., for the required microstructure, especially the pore structure of the storage medium and the particle size distribution of the active storage material, to be destroyed by sintering processes. This leads to aging and subsequently to failure of the battery.